A conventional clutch disc assembly of this type, an arrangement shown in FIG. 5 has already known. In the arrangement of FIG. 5, a hub 100 has an integral outwardly extending outer flange 101 formed therearound. The outer flange 101 has a pair of side plates 102 rotatably disposed at opposite sides of the outer flange 101. The outer flange 101 and side plates 102 have, respectively, formed therein openings 103 and 104 aligned with each other at equal distance in a circumferential direction. The openings 103 and 104 have disposed therein a coil spring mechanisms 105 compressibly in the circumferential direction. One of the side plates 102 is a clutch plate and has fastened thereto a friction facing 106 by way of cushioning plates 107.
According to the above mentioned arrangement, torque of an engine is transmitted to the side plates 102 by way of the friction facing 106, and therefrom to outer flange 101 by way of coil spring mechanisms 105 disposed in the openings 103 and 104, and an output shaft (not shown).
As shown in FIG. l6, in the foregoing arrangement, there are many cases that the coil spring mechanisms consist of concentrically arranged compressible coil springs 110 and 120 of respecitively large and small diameters. The springs 110 and 120 have, respectively, high and low spring constants for a multi-stage characteristic.
However, in such conventional arrangement, because the small diameter spring 110 is compressed during whole stages, compressing quantity of the small diameter spring 110, and therefore the stress thereon, are too large. The small diameter spring 110 may also mesh with the large diameter spring 120 which causes the large diameter spring 120 to the affected when the small diameter spring 110 receives centrifugal force, urging the spring 110 to a radially outer direction.
The small and large diameter springs may be arranged in series (e.g. U.S. Pat. No. 4,690,660).
However, when so arranged the circumferential distance of the openings and the spring mechanisms become large and the outer flange must be designed to maintain durability despite the circumferentially elongated openings. Thus, the arrangement is difficult to carry.